As far as I know, there's no penalty for being silent in this game. I once hosted a game like that and the mafia chose to off all of the active posters and remain silent themselves. I thought to myself hey, everyone can play how they want, it's not my fault if the town decides to take the opportunity to kill themselves! They totally crushed the town, but they were so bored with it that they requested the penalty never be removed again. So I do think inactives are something to consider